Determination of poly(dimethyl)siloxane–water partition coefficients for selected hydrophobic organic chemicals using 14C-labeled analogs (original) (raw)
Related papers
Journal of Chromatography A, 2005
Applications of solid-phase microextraction (SPME) in the measurement of very hydrophobic organic compounds (VHOCs) are limited, partly due to the difficulty of calibrating SPME fibers for VHOCs. This study used a static SPME strategy with a large sample volume (1.6 L) and a five-point calibration procedure to determine the distribution coefficients for a large suite of polychlorinated biphenyls (PCBs) and chlorinated pesticides between a polydimethylsiloxane (PDMS) phase (100 m thickness) coated on a glass fiber and seawater. An extraction time of 12 days was deemed adequate for equilibrium calibration from kinetic experiments. Two groups of randomly selected fibers divided into three batches (up to nine fibers in each batch) were processed separately with two gas chromatography-mass spectrometry (GC-MS) systems. Matrix effects arising from losses of the analytes to glass container walls and stirring bars were corrected. Relative standard deviations within the same batch were generally smaller than those for the entire group. Furthermore, K f V f (K f and V f are the distribution coefficient of an analyte between the polymer-coated fiber and aqueous phase and the fiber volume, respectively) values determined with two GC-MS systems were statistically different. These results indicate the calibrated K f V f values were less affected by the random selection of SPME fibers than by other experimental conditions, and therefore average K f V f values may be used for the same type of commercially available SPME fibers. The relative accuracy of our calibration method was similar to that of a previous study [P. Mayer, W.H.J. Vaes, J.L.M. Hermens, Anal. Chem. 72 (2000) 459] employing different coating thickness and calibration procedure. The present study also obtained a bell-shaped relationship between log K f and log K ow (octanol-water partition coefficient) for PCB congeners with the maximum log K f corresponding to log K ow ∼ 6.5. This bell-shaped relationship was attributed mainly to steric effects arising from the interplay between the PDMS thickness and molecular sizes of the target analytes.
Environmental Toxicology and Chemistry, 2016
Octanol-water partition coefficients (K OW) are widely used in fate and effects modeling of chemicals. Still, high-quality experimental K OW data are scarce, in particular for very hydrophobic chemicals. This hampers reliable assessments of several fate and effect parameters and the development and validation of new models. One reason for the limited availability of experimental values may relate to the challenging nature of K OW measurements. In the present study, K OW values for 13 polycyclic aromatic hydrocarbons were determined with the gold standard "slow-stirring" method (log K OW 4.6-7.2). These values were then used as reference data for the development of an alternative method for measuring K OW. This approach combined slow stirring and equilibrium sampling of the extremely low aqueous concentrations with polydimethylsiloxane-coated solid-phase microextraction fibers, applying experimentally determined fiber-water partition coefficients. It resulted in K OW values matching the slow-stirring data very well. Therefore, the method was subsequently applied to a series of 17 moderately to extremely hydrophobic petrochemical compounds. The obtained K OW values spanned almost 6 orders of magnitude, with the highest value measuring 10 10.6. The present study demonstrates that the hydrophobicity domain within which experimental K OW measurements are possible can be extended with the help of solid-phase microextraction and that experimentally determined K OW values can exceed the proposed upper limit of 10 9 .
Analytical Chemistry, 2000
The determination of distribution coefficients is important for prediction of the chemical pathways of organic compounds in the environment. Solid-phase microextraction (SPME) is a convenient and effective method to measure the distribution of chemicals in a two-phase system. In the present study, the SPME distribution coefficient (K spme) of 16 priority aromatic hydrocarbons (PAHs) was determined with 100-µm poly(dimethylsiloxane) (PDMS) and 85-µm polyacrylate (PA) fibers. The partition coefficients and LeBas molar volumes were used to describe the linearity of the log K spme values of PAHs. Also, the validation of the distribution coefficient was examined using different sample volumes. The extraction time was dependent on the types of PAHs, and 20 min to 60 h was needed to reach equilibrium. The determined log K spme values ranged from 3.02 to 5.69 and from 3.37 to 5.62 for 100-µm PDMS and 85-µm PA fibers, respectively. Higher K spme values of low-ring PAHs were observed using 85-µm PA fiber. Good linear relationships between log K ow and log K spme for PAHs from naphthalene to benzo-[a]pyrene and from naphthalene to chrysene for 100-µm PDMS and 85-µm PA fibers, respectively, were obtained. The correlation coefficients were 0.969 and 0.967, respectively. The linear relationship between log K spme and the LeBas molar volume was only up to benz[a]anthracene for 85-µm PA fiber and up to chrysene for 100µm PDMS fiber. Moreover, the effect of sample volume can be predicted using the partition coefficient theory and excellent agreement was obtained between the experimental and theoretical absorbed amounts of low-ring PAHs. This result shows that the determined log K spme is more accurate than the previous method for estimating analytes with log K ow < 6 as well as for predicting the partitioning behaviors between SPME fiber and water. The physicochemical data of xenobiotic compounds are usually used to predict their environmental fate and effects and that of compounds with similar physicochemical properties. Hydorphobicity is one of the most important parameters governing the distribution behavior of xenobiotics in the environment. The octanol-water partition coefficient (K ow) is widely accepted as the
Journal of Chromatography A, 2007
Water-to-polydimethylsiloxane (PDMS) and gas-to-PDMS sorption coefficients have been compiled for 170 gaseous and organic solutes. Both sets of sorption coefficients were analyzed using the Abraham solvation parameter model. Correlations were obtained for both "dry" headspace solid-phase microextraction and conventional "wet" PDMS coated surfaces. The derived equations correlated the experimental water-to-PDMS and gas-to-PDMS data to better than 0.17 and 0.18 log units, respectively. In the case of the gas-to-PDMS sorption coefficients, the experimental values spanned a range of approximately 11 log units.
Environmental Toxicology and Chemistry, 2009
The aim of the present study was to develop a passive absorptive equilibrium sampler that would enable the determination of the concentrations of polar organic compound (POC) in water more efficiently than existing techniques. To this end, a novel plastic material, poly(ethylene-co-vinyl acetate-co-carbon monoxide) (PEVAC), was evaluated and the results were compared with an existing silicone-based passive absorptive equilibrium device. Seven compounds (imidacloprid, carbendazim, metoprolol, atrazin, carbamazepine, diazinon, and chlorpyrifos), a mixture of pharmaceuticals, and pesticides with a logarithmic octanol-water partition coefficient ranging from 0.2 to 4.77 were selected as model substances for the experiments. The results showed that six of the seven selected POCs reached distribution equilibrium within 4 d in the two materials tested. A linear relation with a regression coefficient of more than 0.8906 between the established logarithmic absorbent-water partition coefficient and the calculated logarithmic dissociation partition coefficient of the selected compounds in the two polymers was observed. The correlation between these two coefficients was within one order of magnitude for the compounds that reached equilibrium in the two polymers, which demonstrates that both materials are suitable for mimicking biological uptake of POCs. The PEVAC material showed an enhanced sorption for all selected compounds compared to the silicone material and up to five times higher enrichment for the most polar compound. Fluorescence analysis of the sampler cross-section, following the uptake of fluoranthene, and proof that the sorption was independent of surface area variations demonstrated that the PEVAC polymer possessed absorptive rather than adsorptive enrichment of organic compounds.
Chemosphere, 2010
With increasing ionic strength, the aqueous solubility and activity of organic chemicals are altered. This so-called salting-out effect causes the hydrophobicity of the chemicals to be increased and sorption in the marine environment to be more pronounced than in freshwater systems. The process can be described with empirical salting-out or Setschenow constants, which traditionally are determined by comparing aqueous solubilities in freshwater and saline water. Aqueous solubilities of hydrophobic organic chemicals (HOCs) however are difficult to determine, which might partly explain the limited size of the existing data base on Setschenow constants for these chemicals. In this paper, we propose an alternative approach for determining the constants, which is based on the use of solid phase micro extraction (SPME) fibers. Partitioning of polycyclic aromatic hydrocarbons (PAHs) to SPME fibers increased about 1.7 times when going from de-ionized water to seawater. From the log-linear relationship between SPME fiber-water partition coefficients and ionic strength, Setschenow constants were derived, which measured on average 0.35 L mol À1. These values agreed with literature values existing for some of the investigated PAHs and were independent of solute hydrophobicity or molar volume. Based on the present data, SPME seems to be a convenient and suitable alternative technique to determine Setschenow constants for HOCs.
2006
A depletion solid-phase microextraction (SPME) method for the characterisation of SPME sorption for 13 pesticides selected as probe compounds is described. The sample is extracted and analysed multiple times by SPME-GC/MS. The observed depletion in peak areas is used for the calculation of extraction ratios that varied between 3 and 28% for a PDMS fiber with confidence intervals between 0.7 and 5.4%. Apparent fiber-sample partition coefficients can be calculated and extrapolated to equilibrium conditions if specific sorption kinetics are known. Under the chosen conditions, problems were encountered for more polar compounds (log K ow < 3) due to inefficient extraction. The extracted amount was found to be the decisive parameter for depletion SPME and the extraction conditions therefore need to be adapted to the polarity of the analyte. The importance of the initial analyte concentration especially for mixed-mode fibers is demonstrated. Compared with conventional external calibration using liquid injection, depletion SPME eliminates uncertainties due to solvent effects during injection. Furthermore, it does neither require authentic reference compounds nor knowledge of the initial analyte concentration, and thus can even be used for unknowns.